Throughput enhancement of a slotted DS-CDMA ALOHA with packet combining

An adaptive time-diversity automatic repeat request scheme is investigated for a slotted DS-CDMA wireless data network over frequency selective Rayleigh fading channels. In the proposed technique, the receiver retains and processes all the retransmissions of a single data block using postdetection diversity combining rather than simply discarding the noisy packets. It is shown that packet combining is an effective mechanism for enhancing the network throughput and delay performance of a conventional DS-CDMA ALOHA, while sustaining a reasonable receiver complexity. This scheme is highly advantageous for systems which can tolerate a certain delay and operate over highly time-varying channels. We also examine the effects of forward error correction (FEC) coding and multipath intensity profile on channel utilization efficiency